Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus for a semiconductor substrate.
Description of the Related Art
In order to reduce the on resistance of a semiconductor power device, there have been proposed various trench FETs using a silicon carbide (SiC) substrate (see Japanese Patent Application Laid-open No. 2013-077761, for example). As to such trench FETs, a trench formed in a semiconductor substrate by dry etching treatment using a dry etching apparatus or the like is known to have sharp corners at the opening and the bottom thereof.
The sharp corners at the trench sometimes causes coating defects at the time of coating of a gate insulation film, leading to the occurrence of voids when an electrode embedded into the trench is formed, and, as a result, significantly affects device characteristics of the semiconductor device. In addition, the sharp corners at the trench may cause electric field concentration leading to a problem of the gate insulation film such as an electrical breakdown, and thus the improvement is being demanded.
To address this, there has been proposed a method to ensure reliability of the gate insulation film by making the sharp corners at the opening and the bottom of the trench rounded to ease the electric field concentration (see Japanese Patent Application Laid-open No. 2008-177538). Japanese Patent Application Laid-open No. 2008-177538 discloses that a process of making the sharp corners at the opening and the bottom of the trench rounded involves first heat treatment in an Ar gas atmosphere or a SiH4 gas/inert gas atmosphere in a temperature range of 1600° C. to 1800° C., inclusive, and a second heat treatment in a hydrogen atmosphere at 1400° C. to 1500° C., inclusive.